Re: ATM !! HELP!!! FIGURING HELP POLISHING!!!

[Brad Davy <bdavy@fred.net>]

Dear sir, 

While many of us on this list have been at your stage, please refrain
from disparaging the group.  You are not the first, and certainly not
the last person who has had this problem.  

Polishing and figuring are separate processes.  First you must polish
the mirror into a spherical shape.  You will best accomplish that by
placing the tool on top of the mirror, doing a long cold press with only
the weight of the tool (over night), then using 1/3 Center over Center
strokes.  Keep turning the tool opposite the direction you walk around
the mirror.  Turn the mirror as well in the opposite direction.  Press
down on the tool with your hands between the center and the edge of the
tool.  This should take about 1 hour for each inch of diameter of the
mirror.  Only use a thin mixture of CeO.  If the polishing action stops
(the mirror isn't squealing when you polish), separate the two, scrub
the face of the lap with a brass wire brush, cold press again overnight,
then resume.  You may only want to polish for 30-60 minutes per night. 
This is hard work.

Once you have COMPLETELY polished the mirror (no surface defects or very
tiny pits visible with a magnifying lens, reversed eyepiece, laser
pointer), then you are ready to perform the first test, which should
simply be to determine the spherical null with a focault or ronchi test.

When you reach a sphere, then you are ready for figuring.

Figure in short sessions (5 minutes or less).  Use wide W strokes (4/5)
turning both the tool and the mirror as you walk around the barrel. 
After a 5 minute figuring session, set the mirror in the test stand, and
wait until the next night to test.  This will ensure thermal
equilibrium.  Test the mirror and plot your figure using any of the
several programs that are available.  Print these out so you can
reference them from session to session.

There are MANY variations and tricks to treating the MANY different
problems you can encounter.  Search the ATM archives.  You may have
recieved the archive address when you subscribed to the group.  The
archives cover over 5 years worth of messages, and are an invaluable
tool, especially for the first timer.  

You may want to consider getting a copy of "How to make an astronomical
telescope" by Jean Texereau, available from Willman-Bell.  Its a time
tested reference.  There are many shortcuts that have been developed
over the years, but Tex is still a very worthwile reference.

Finally, should you feel it necessary to vent at the list again, I can
assure you that no one on this list will respond with any worthwhile
advice, and you will probably be removed by the list owner.  This list
is an extremely civil forum, and we want to keep it that way.